Water Quality

1 WFD Overall Physio-Chemical Quality Elements

Within the Avon Bristol Urban’s 14 individual EA waterbodies. In the most recent WFD classification in 2022, 7% of waterbodies scored “Good” for Physio-Chemical Quality Elements, whilst 0% of waterbodies scored “High”.

In comparison the 2019 WFD classification saw: 14% of waterbodies scored “Good” for Physio-Chemical Quality Elements, whilst 0% of waterbodies scored “High”.

Physio-Chemical Quality Elements include the following items:

  • Ammonia (Phys-Chemical)
  • Dissolved oxygen
  • Temperature
  • Biochemical Overall Oxygen Demand (BOD)
  • Phosphate
  • pH
  • Acid Neutralising Capacity

This page does not visualise Acid Neutralising Capacity, pH or Temperature elements.

1.1 Reasons for Not Acheiving Good

The below table shows RNAGs which either have a Phys-Chem classification element or either of their main pressures as nutrients or Phys-Chem elements.

Tip

Use the below ‘Search’ box to to search for a waterbody or classification element and scroll through RNAGs and Measures. Click the ‘Excel’ button to download a spreadsheet.

1.2 Measures

Measures for the waterbodies identified above are shown in the table below.

2 Pressures

2.1 Point Source Pollution

The below map provides the whereabouts of continuous permitted WWtW and their likelihood of eutrophication, as well as the option to view intermittent CSO discharges for 2023. These provide some indication of the loading from point source pollution on waterbodies. Point source pollution from fish farms and private consented discharges are not mapped here but can be found on easimap.

Wessex Water Continuous and Intermittent sewage discharges

2.2 Diffuse Source Pollution

The below map shows data from the Agricultural Land Environmental Risk Tool (ALERT), it models diffuse pollution pathways and simulates their diffuse pollution risk. Created by the Geomatics team, EA, it is commonly used by agricultural teams in farm visits, the diffuse pollution risk scores are modelled on:

  • Land-use (2021)

  • Hill slope

  • Erosion and runoff risk of soil

  • Mean precipitation

The below map provides a mean score of diffuse pollution per waterbody using the data from ALERT, for further granularity, you can view diffuse pollution pathways at a reach scale. This data is indicative of erosion risk and doesn’t reflect actual risk, which can only be identified through monitoring.

Diffuse pollution pathways data taken from the Agricultural Land Environmental Risk Tool

3 Monitoring data

Here we select a few physio-chemical elements, these although traditionally used for WFD WQ monitoring, are only a cross section. They don’t include emerging chemicals such as caffeine, anti-depressants etc. These are partly covered by priority substances or not monitored for at all. Furthermore, the impact of multiple interacting chemicals, “chemical cocktails” are also not considered here.

In order to give a monitoring overview, the below pop-up plots show data over the last 5 years, this includes the interim WFD classification in 2022, at both a waterbody and site level. From 2022 to current, where no WFD classification is calculated, monitoring site data is still provided as boxplots and as a map.

Orthophosphate reactive as P (PO4-P) monitoring sites are grouped together per waterbody within the catchment in the plot shown below. Horizontal lines indicate “poor” and “good” WFD site classifications. Mean sample orthophosphate readings are shown for individual monitoring sites in the map below. Both plots show the most recent monitoring from 2022-2025.

Nitrates are primarily introduced into freshwater through agricultural runoff, wastewater discharge and septic tanks. Excess nitrates lead to algal blooms, low oxygen levels. Nitrites are typically present in smaller quantities than nitrates, although they are more toxic to aquatic organisms than nitrates. Nitrities are unstable and convert between ammonia and nitrate.

Ammonia is highly toxic to fish and aquatic organisms, it becomes more toxic at higher pH and water temperatures.

BOD is calculated using 90th percentiles, here, the blue line on the boxplots indicates the 90th percentile.

BOD measurements from “crude sewage”, “final sewage effluent” and “storm sewer overflow discharge” are omitted as to not skew the river sites on the map with localised, regulatory scores.

3.1 Third Party Data

This initial evidence pack doesn’t include any water quality Water Company data, only citizen science data taken directly from the Angling Trust’s water quality monitoring scheme (currently one of the easiest national Citizen Science schemes to get WQ data from). Third-parties often have a different or un-aligned monitoring agenda to the Environment Agency. Eventually through influence, priorities can be aligned however, initially data may not be exactly where the EA would require it.

[1] "The Avon Bristol Urban does not have any monitoring data collected in the Angling Trust's Water Quality Monitoring scheme to display"